A new fossil of a giant predatory dinosaur has shed light on the North American ecosystem during the Cretaceous period. The new species, Siats meekerorum, is a member of the allosaurs, a group of large predators that predate the tyrannosaurs that dominated later in the Cretaceous. By filling in a gap in the fossil record, Siats has helped paleontologists understand the changes that took pace during the transition between these groups of apex predators.

The fossil of Siats isn't going to be the centerpiece of a museum display; the bones that are available are largely from the spinal column, accompanied by a few of the limb bones and a variety of other fragments. Fortunately, the allosaurs are well-known from examples on other continents, and the skeletal fragments show a clear relationship to a specific group of allosaurs called the carcharodontosaurs. This allows the paleontologists who discovered it to infer things about the physical appearance of the body parts that haven't yet been found.

Although only a juvenile, the beast was probably already 30 feet long and was likely to weigh four tons. Depending on how much it grew later, it could have ended up being truly enormous. This makes some sense, given that another of the carcharodontosaurs found in Argentina has been named Giganotosaurus due to its enormous size. However large it grew, it was clearly an apex predator during its time in North America.

(In fact, the genus name derives from Siats, a predatory, man-eating monster from legends of the Ute native tribe of Utah.)

And that time turns out to be rather interesting, somewhere in the middle of a 70-million-year gap in which there was a grand total of one large predator that we know to have resided in North America. The new fossil indicates that North America was progressing much like the rest of the continents, with the carcharodontosaurs sitting squarely atop the food chain. The authors of the paper describing it even consider the prospect that, despite the elevated ocean levels of the time, the continents might not have been as isolated as we think they were, and dominant groups may have made their way among them.

In any case, the fossil provides some support for a model of how the carcharodontosaurs ended up being replaced. They may have been the top predators around, but there were certainly others, including some small species of tyrannosaurs that have been found in fossil layers that date from roughly the same time. That's led the authors to propose that the apex predators were to tyrannosaurs what dinosaurs in general were to mammals.

"The huge size difference certainly suggests that tyrannosaurs were held in check by carcharodontosaurs and only evolved into enormous apex predators after the carcharodontosaurs disappeared," said Peter Makovicky. In other words, something had to kill the large carcharodontosaurs off for the tyrannosaurs to take their place as the apex predators of North America. We don't know what that something was, but if we ever find out, all the kids who have grown up as fans of T. rex can send it a thank-you note.

Pretty bad headline even for Ars, considering these had no crossover with Tyrannosaurus Rex by tens of millions of years (rtfa).

I'll just leave this here...

tfa wrote:

In any case, the fossil provides some support for a model of how the carcharodontosaurs ended up being replaced. They may have been the top predators around, but there were certainly others, including some small species of tyrannosaurs that have been found in fossil layers that date from roughly the same time. That's led the authors to propose that the apex predators were to tyrannosaurs what dinosaurs in general were to mammals.

"The huge size difference certainly suggests that tyrannosaurs were held in check by carcharodontosaurs and only evolved into enormous apex predators after the carcharodontosaurs disappeared," said Peter Makovicky. In other words, something had to kill the large carcharodontosaurs off for the tyrannosaurs to take their place as the apex predators of North America. We don't know what that something was, but if we ever find out, all the kids who have grown up as fans of T. rex can send it a thank-you note.

"Yes... yes. This is a fertile land, and we will thrive. We will rule over all this land, and we will call it... This Land.""I think we should call it... your grave!""Ah! Curse your sudden but inevitable betrayal!""Ha ha ha! Mine is an evil laugh! Now DIE!""Oh no, God, oh dear God in heaven..."

Mercury and Venus have no plate tectonics for they are so closed to the Sun all liquid water had evaporated.

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With that said, bottom line is: When there's no plate tectonics, there would be no ocean, no water, and so no lives, no dinosaurs, no evolution.

I can't follow your logic here. Plate tectonics are a result of radioactive decay inside the planet. Radioactive decay creates heat, which melts the rock and the crust floats around on it. It has absolutely nothing to do with being close to the sun or not having an ocean.

It's perfectly conceivable that a planet with liquid water oceans being one AU from their sun might have no internal radioactive decay, and therefore no plate tectonics.

Mercury's plates haven't melted together, if that's what you're trying to say. That would make Mercury a ball of lava instead of rock! Dooza's question was perfectly rational.

Great. This just tacked four extra months of development time onto Jurassic Park 4 aka Jurassic World. Because we need only the biggest, scariest fucks to throw at Iran.(I actually know nothing about that movie, but I assume this will be in it. Regardless of this creature's native period.)

Excellent.So, first Tyro is a ferocious hunter, then he's a scavenger, lately he's a bumbling idiot. Now we have the Tyrannosaur killer! Except, maybe, in a few decades some bright spark will claim, "oops, sorry everyone, chill, he was just the result of a fermented-Triceratops-blood-fueled dino orgy!"

At least we still have some time: allosaurus was around I think 5mil years (155m to 150m years ago, from wiki), while tyrannosaurus was also around few million years ... while modern humans are around only some 100k years .

But if humans became apex predators even before modern humans (if Homo erectus was also apex predator), then we 'used' over 1mil years already ;p

"The huge size difference certainly suggests that tyrannosaurs were held in check by carcharodontosaurs and only evolved into enormous apex predators after the carcharodontosaurs disappeared,"

Or Tyrannosaurids simply needed to develop the genetic codes for reaching these huge sizes. They seemed to have some inherent advantages for smaller sizes early on and perhaps they just needed a couple million years to develop the genetic codes for reaching big sizes. (Which the Carcharodontosaurs already had)

Or still alternatively the Carchadontosaurs were adapted to hunting something big that dissapeared. (Sauropods) once the big prey became faster and more nimble ( triceratops etc.) suddenly the Tyrannosaurids did win out.

In the end I do not believe in the "keeping in check" thing. This may be true for totally different habitats like mammals which were kept out completely of the big animal spots. But for different sizes of big predators I think there must be some inherent genetical advantages.

This always repeating depiction of apex predators with their mouths wide open is ridiculous. This one is even drooling. It entertains the same inane perception like we are unfortunately used to get from shark images. Fierce creatures preying all day long.

Why do artists still stoop to such behavior ? They should know better in the meantime. Sigh.

This always repeating depiction of apex predators with their mouths wide open is ridiculous. This one is even drooling. It entertains the same inane perception like we are unfortunately used to get from shark images. Fierce creatures preying all day long.

Why do artists still stoop to such behavior ? They should know better in the meantime. Sigh.

I don't mind the "mouth open" part because at least it lets the viewer get a better appreciation of the business end of these things. What I don't really care for is the depictions (e.g. Walking With Dinosaurs) where they run around stamping their feet at things and roaring every three seconds.

This always repeating depiction of apex predators with their mouths wide open is ridiculous. This one is even drooling. It entertains the same inane perception like we are unfortunately used to get from shark images. Fierce creatures preying all day long.

Why do artists still stoop to such behavior ? They should know better in the meantime. Sigh.

EnticingHavoc wrote:This always repeating depiction of apex predators with their mouths wide open is ridiculous. This one is even drooling. It entertains the same inane perception like we are unfortunately used to get from shark images. Fierce creatures preying all day long.

Why do artists still stoop to such behavior ? They should know better in the meantime. Sigh.

Because when you have that many teeth you have that big of a mouth to match them. Artists don't just making up image like this one has. They did this drawing by the suggestions of the scientists.

I wonder, if there are life sustaining planets, and life arises there, would evolution follow the same kind of path there as it does here.

Based on my very limited layman's knowledge of physics, chemistry, and biology, I think the only thing we can say with any confidence is that any life we find will look similar at the molecular level (i.e., carbon-based, using many of the same molecules we use, just because carbon-based chemistry seems to be ubiquitous); above that, all bets are off.

Depending on the environment, we could expect some convergence; for example, we could probably expect any large, fast, pelagic (open-water) swimmers to look like Earthly fish or cetaceans (long, streamlined, with some fins for stabilization), simply because such a form is efficient for that environment. Whether their internal anatomy bears any relation to Earthly vertebrates is another question entirely. Similarly, there would probably be burrowers, flyers, non-pelagic swimmers, etc., and those environments would probably drive many of the same adaptations we see here.

Whether that leads to recognizable vertebrates, or quadrapeds, or even bipedal naked apes is very much an open issue. I wouldn't expect that level of convergence, myself. Hell, I wouldn't expect recognizable kingdoms (plants vs. animals vs. fungi vs. archae).

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And if it does, are there certain things that may lead to equilibrium that puts a brake on evolution. Say, lack of plate tectonics. Or a single land mass.

Nothing puts a brake on evolution, simply because there's always noise in the reproductive process. There's always going to be some level of drift, even if there aren't any significant changes in selective pressures.

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The only reason I ask this, is I often wonder how this planet's evolutionary path would have panned out say if there was only a single land mass and no pate tectonics.

It may be that the envronment changes more slowly, so evolutionary changes are driven more by drift than selective pressures. Or it may not make a difference, depending on how the planet's axis precesses, how eccentric its orbit is, how that eccentricity changes over time, etc.

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I'm sure life would evolve, but a lot slower if there was no islands that moved around the globe and drove evolution forward.

Would we still have dinosaurs today?

We do, they're just a lot smaller and less toothy than they used to be.

Ooo don't open that door... creationists and evolutionistsnon-retarded people get their bits in knots over that. Especially don't suggest that Carbon Dating could be flawed, that'll get you lynch-mobbed...since anyone using carbon dating to date something without carbon in it must be a creationist.